Loudspeaker



Dec. 20, 1955 J, a LOKKESMOE 2,727,949

' LOUDSPEAKER Filed Sept. 22, 1951 IZ g. .Z

12 fig 2 INVENTOR.

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H 5 ATTORNEYS United States Patent-O LOUDSPEAKER Julius B. Lokkesmoe,Berkeley, Calif. Application September 22, 1951, Serial No. 247,779 4Claims. (Cl. 179-1155) My invention relates to improvements inloudspeakers, and particularly to loudspeakers of the electro-dynamictype.

An object of my invention is to provide a novel and improvedelectro-dynamic loudspeaker having high fidelity response at both thelow and high frequency ends of the audio frequency range.

Another object is to provide novel and improved means for improving thelow frequency response of an electrodynamic loudspeaker.

This and other objects of my invention together with various advantagesthereof are set forth in the following description of the embodiment ofmy invention illustrated in the accompanying figure wherein:

Fig. 1 is a partially sectional view of my improved loudspeaker; and

Fig. 2 is a wiring diagram of a circuit employed in connectiontherewith.

in Fig. 1 there is illustrated an electro-dynamic loudspeaker embodyingmy invention. This loudspeaker comprises a conventional type resilientlymounted coneshaped diaphragm 12 having a cylindrical voice coil 14mounted coaxially at the apex thereof, and a permanent magnet structure16 involving a stem or pin 18 projecting a short distance into the voicecoil 14, and tapered pole tips 20 opposite the free end of the pin,externally of the voice coil. The free end of the pin 18 and the poletips 20 define a gap in which the voice coil is free to move in responseto currents flowing through the voice coil.

In order to render such a loudspeaker efiicient in transformingelectrical energy into acoustical energy, the voice coil 14 is normallyof light weight compared to the weight of the diaphragm 12. Suchloudspeakers, however, are normally inherently deficient in the regionscovering both the low and high frequency ends of the audio frequencyrange and particularly at frequencies in the range below about 100 to125 cycles per second. In that low frequency range, such loudspeakersgenerally attenuate the low frequency sounds to such an extent that thedeficiency requires remedy of some sort in order to attain highfidelity.

According to my invention high fidelity of such a loudspeaker isattained by mounting an auxiliary coil upon the pin 18 in magneticallycoupled relationship to the voice coil and connecting this coil in atuned circuit that is electrically connected in parallel to the voicecoil. With this arrangement I find I am able by adjusting the frequencycharacteristic of the circuit, to not only improve the low frequencyresponse, but also the high frequency response of the speaker at thesame time.

As illustrated in Fig. 2 a condenser 22 connected in series with theauxiliary coil 21, forms a series tuned circuit 24 that is connected inparallel with the voice coil 14 across the secondary winding 26 of anoutput transformer 28. The resonant frequency of the tuned circuit 24depends in part upon the inductance of the coil 21 and the inductancesof the voice coil 14 and the effective inductance of the secondarywinding 26 looking into the transformer 28 from the output side thereof.The value of the condenser 22 is so chosen relative to the values of thethree inductances mentioned that it tunes the circuit 24 to a low audiofrequency of about 25 to 30 cycles, thus causing the currents flowing atlow frequencies in the tuned circuit 24 to be emphasized compared withcurrents flowing at other frequencies. Inasmuch as the voice coil 14 isinductively coupled to the auxiliary coil 21, increased currents flow atsuch low frequencies in the voice coil as well as in the auxiliary coil,the flux produced by such low frequency currents being confined to themagnet structure.

It appears, however, that at the high frequency end of the audiofrequency range, the flux is no longer confined entirely to the magnetstructure. An increasing amount of the coupling between the auxiliarycoil and the voice coil becomes air coupling, thus cutting down the ironlosses and thereby permitting the higher frequency currents to be ofgreater magnitude and freer from distortion. In this manner, the higherfrequency response is enhanced. The auxiliary coil is preferably ofhigher inductance than the voice coil, thereby reducing the magnitude ofthe capacitance required of the condenser 22 in order to tune thecircuit to the desired low frequency.

The mutual inductance of the coupling may be either positive ornegative, depending upon whether the two coils 14 and 21 are wound inthe same direction or in the reverse direction on the pin 18, whenconsidered with reference to their connections to the secondary winding26. While either of these arrangements is effective, I prefer to windboth coils in the same and preferably clockwise direction on the polepin, looking in the direction of the cone.

From the foregoing description of my invention, it is apparent that Ihave provided a novel and improved electro-dynamic loudspeakerarrangement in which higher fidelity is achieved by improving thefrequency response characteristics at both ends of the audio frequencyrange. While my invention has been described with reference to aparticular structural arrangement of an auxiliary coil upon the pin of amagnet of an electro-dynamic speaker, it is to be understood thatvarious modifications of my invention may be made without departing fromthe principles of my invention. It is therefore intended to cover allsuch modifications thereof that fall within the scope of the appendedclaims.

I claim:

1. In combination with a loudspeaker employing a diaphragm driven by amovable voice coil that is mounted in the gap of a magnet, saiddiaphragm and coil having a response characteristic that falls off atlow sound frequencies, a tuned circuit involving a stationary coilfixedly mounted on said magnet, said circuit being tuned to a lowfrequency of the order of 25 cycles per second whereby due to themagnetic coupling between said coils at such low frequency resultingfrom the fixed mounting of said stationary coil on said magnet, the lowaudiofrequency currents through said voice coil will be emphasized.

2. In combination with a loudspeaker employing a diaphragm driven by amovable coil that is mounted in the gap of a magnet, a condenser and aninductance connected in series across said movable coil, said inductancebeing formed by a stationary coil fixedly mounted on said magnet andinductively coupled at low audiofrequencies to said voice coil by saidmagnet whereby low audio-frequency currents will be emphasized.

3. A sound reproducing system comprising a magnet formed with a ga amovable coil mounted in said gap and arranged to drive a diaphragm, astationary coil fixedly mounted on said magnet, the inductance of saidlow irequency' in the audio. range whereby due to the magnetic couplingat such, low audio-frequency between said; coils. resulting from thefixed mounting of said stationary coil on said magnet, the lowaudio-frequency currents through said, voice coil will be emphasized.v

4. A sound reproducing system comprising a magnet formed with a'gap, amovable coil mounted in said gap and. arranged to drive a diaphragm, astationary coil fixedly mounted on ,said magnet, the self inductance. ofsaid stationary coil being large in comparison with the self inductanceof said movable coil, and a circuit tuned to a low frequency in theaudio range. and formed in part by said stationary coil being connectedin series across said movable coil whereby due to the magnetic on saidmagnet, the low audio-frequency currents through said voice coil will beemphasized.

References Cited in the file of this patent UNITED STATES PATENTS1,830,402 Miessner Nov. 3, 1931 1,868,607 Kolster July 26, 19321,878,232 Chromy Sept, 20, 1932 2,004,735 Thomas June 11, 1935 2,007,746Ringel July 9, 1935 2,007,748 Olson July 9, 1935 2,007,749 Anderson July9, 1935 2,269,284 Olson Jan. 6, 1942 2,286,123 Steers June 9, 1942

